More carbon dioxide makes plants picky about their fertilizer

Researchers have found that plants that are given an excess of carbon dioxide …

The concentration of carbon dioxide in the atmosphere continues to ramp up, but maybe that's not all bad—plants will love it, right? Not necessarily, according to a study published this week. Researchers have found that an increase in ambient carbon dioxide actually inhibits plants' assimilation of nitrate from the soil, meaning they can't process a larger carbon dioxide load when this is their primary source of nitrogen.

In the experiment, scientists tried five different soil and atmosphere combinations on wheat and Arabidopsis, a member of the mustard family. The plants were exposed to various combinations of plain and nitrate-enriched soil, and atmospheres with normal and elevated carbon dioxide levels.

The results showed that it didn't matter to the plants how much nitrogen or carbon dioxide they were exposed to, as they assimilated the same amount regardless of the environment. This is notably different from when the plants are supplied with nitrogen via ammonium, which, in combination with excess CO2, can stimulate growth. The authors speculate that this difference is due to the biochemical mechanisms that the plants use to incorporate nitrates into biomolecules.

Researchers point out that plants may yet adapt to increased carbon dioxide levels, but there would still be a drawback—once they can use all that carbon dioxide, they will need to pull more and more nitrate from the soil. We may be able to lean on ammonium- and nitrate-based fertilizers to restore the soil's balance, but that would increase our reliance on fertilizers, which have their own issues.